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# 12.3 intro to probability

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### 12.3 intro to probability

1. 1.  The probability of an event is how likely it isto occur. Is a number between 0 and 1. Probability of 1: event is certain to occur. Probability of 0: event will never occur. Probability of ½: equally likely to occur or not.
2. 2.  When all outcomes are equally likely, thetheoretical probability that an event A willoccur is: Can be expressed as a fraction, decimal, or %.
3. 3.  You roll a six-sided die with sides numbered1 through 6. Find the probability of: rolling a 4. rolling an odd #. rolling a # less than 7.
4. 4.  A spinner has 8 equal-size sectionsnumbered 1 though 8. Find the probabilityof: spinning a 6. spinning a # greater than 5.
5. 5.  You put a CD that has 8 songs in your CDplayer and set it to random. The player playsall 8 songs without repeating any song. What is the probability all songs are played inthe same order listed on the CD? What is the probability that 2 of your 4favorite songs are played first, in any order?
6. 6.  There are 9 students on the math team. Youdraw their names one at a time to determinetheir order at the competition. What is the probability that 3 of the 5 seniorson the team will be chosen last?
7. 7.  Five cards are drawn from a 52-card deck.What is the probability that the first two cardsare red?
8. 8.  It is not always possible to find theoreticalprobability. Can sometimes find the experimentalprobability using an experiment, survey, orhistory of the event.
9. 9.  In 1998, a survey asked internet users fortheir ages. Find the exp. probability that arandomly selected internet user is: at most 20 years old? at least 41 years old?Age # of usersUnder 21 163621 -40 661741 – 60 369361 – 80 491Over 80 6
10. 10.  Found by calculating the ratio of two lengths,areas, or volumes. Example: Find the probability that a randomly throwndart would hit the shaded region.4
11. 11.  You have a 2 hour movie recorded at thebeginning of a tape that holds 6 hours ofrecordings. Your brother randomly records a30 minute show on the tape. What is theprobability that his show records over part ofyour movie?
12. 12.  A store is open from 8 am to 8 pm. Themanager works 9-4. What is the probabilitythat the manager is there during a randomcustomer’s 15 minute visit?
13. 13.  The target for a bean-bag toss game is arectangle 3 ft wide and 4 ft tall with 3 circularholes, each with radius 1 foot. What is theprobability that a random bean-bag will passthrough one of the holes?